Racing Bolt Technology

1/9This huge torque wrench has no place on a small bolt like this one; we just thought it looked cool. Torque values vary depending on the application and dimension of the bolt, as we will learn.

For many racers, nuts and bolts are some of the most misunderstood parts on the car. Many of us do not really know a great deal about these fasteners in general. We might misuse them or make poor selections.

Engine hardware aside, we tend to not really consider the role of a nut or a bolt until it breaks and causes another serious issue. For example, a bolt that holds a weight onto the chassis fails during a race, and the weight falls off the car as a result. You win the race, not necessarily because a 5-pound weight fell off. The tech inspectors find that you were light across the scales after the race, and you are disqualified. A 10-cent bolt causes you to lose a hard-earned victory.

This is an issue that can cause some real grief. It's a very simplistic illustration, but the issues could be much greater (e.g., a suspension system failure). These situations are completely preventable if we learn how to select the right hardware for the given application.

Back in high school, we were introduced to simple machines in science class: the lever, inclined plane, wedge, wheel, axle, and screw. There are really only five simple machines, as the screw is just an inclined plane wrapped around a rod. The thread itself is a variation of the inclined plane.

From a racer's perspective, bolts and nuts are the primary method for holding the car together. We start with a frame of welded tubes and sheetmetal, but the remainder of the ancillary parts are held in place primarily with nuts and bolts, or possibly some rivets.

2/9The components of a bolt are not that complex. Once you know the nomenclature, it is no big deal. If you want a 51/416x18x111/42-inch bolt, 51/416 is the diameter in inches, 18 is the number of threads per inch pitch, and 111/42 is the length in inches.

Let's spend some time examining how bolts really work. What happens when you tighten a bolt or run a nut down on a stud and torque it into place? A bolt or a stud turns into a spring that exerts a load on the parts you are trying to hold together when it is tightened. It is not that difficult to imagine.

The bolt stretches as it is tightened. As long as you do not tighten it past the point where the metal the bolt is made from yields or breaks, the bolt will exert force as the result of it trying to return to its free state. A collection of springs trying to get back to a free state holds your race car together. This force can be significant; in fact, if you use multiple bolts or studs, the amount of load or clamping force they can place on the structure is quite high.

From both a physical and material perspective, bolts are very well-defined parts. From a performance perspective, there are specifications for multiple characteristics of the bolt: load, grip, shear forces, clamping force, and tension force. The characteristics of the bolt from a manufacturing perspective are also very well defined and highly controlled. Bolts are not as simple as they seem. A good bit of engineering has gone into developing threaded fasteners.

Once you have established the need for a bolt and determined the forces the bolt will endure, you can derive which bolts and nuts you need for a specific application. Points to consider include the following: hex size (the wrench size used to drive the bolt, or this can also be an internal hex drive), length, thread length, thread pitch, and nominal diameter.

3/9Grade 5 bolts have three lines stamped in the head of the bolt. This level is the minimum that should be used on the race car. Typical uses include holding on body parts, lightweight attachments such as tachometers and ignition switches, and so on. Never use this grade to bolt structural components together.

Bolts are also classified by grade (i.e., the level of material used to make the bolt and the amount of heat treatment it has been exposed to). We select a bolt for a given application according to its grade. The most common grades range 2 through 8, with Grade 8 being the hardest and the strongest.

Unfortunately, many racers just use what they have on hand and are not too concerned about grades or specifications. While this is the accepted norm, the proper selection can save you more than money. It could save you from a failure that may have more dire consequences.

Bolts are graded against a scale developed by the SAE (Society of Automotive Engineers). The rating scale starts at Grade 2. Grade 2 bolts are made of low-carbon steel and are usually zinc plated (silver in color). There are no markings on the head of a Grade 2 bolt (more on this later). This grade is usually found in hardware stores and intended for use in low-strength applications, such as gates and fences.

This type of bolt has no place on a race car. Not to say that this grade may not be used to attach sheetmetal panels to each other or be used for some other low-load requirement. The main reason this grade shouldn't be used on a race car is that it may find its way into an application that requires a fastener with a higher grade.

In an emergency situation on the track, use of this grade bolt could be downright dangerous. The best way to prevent this is to make sure that Grade 2 bolts are never on your race car.

4/9For structural or chassis mounting, use Grade 8 or better bolts. These have six lines stamped into the head. Typical uses include bolting on upper control arms, sway bar arms, rear trailing arms, and so on.

Grade 5 bolts are manufactured from a medium grade of carbon steel. They are also zinc plated and heat treated to a tempered state. This is the minimum grade that should be used in race car applications. Grade 5 bolts are easily identified by the three raised lines on the head of the bolt. As the Grade 2 bolts have no markings on the head, the addition of three lines on the head of the Grade 5 bolt (2+3=5) make it easily identifiable.

Good selections of Grade 5 bolts can be found in the hardware sections of local home improvement stores and better hardware stores. Most auto part stores carry them as well. There is also a plethora of hardware sources on the Internet. The only problem with the Internet sources is that you have to know exactly what you want. It is more difficult to browse the hardware section and impossible to touch the product on the Internet. Grade 5 bolts are reasonably priced and have sufficient strength for most of the non-engine-related and non-structural functions on a race car.

Grade 8 bolts are manufactured from a carbon alloy steel and are also plated with zinc, but they usually have a yellow or gold hue (although some are silver colored). They have been heat treated to a higher level and are much harder. There are six lines on the head of a Grade 8 bolt. If you have an application that requires a good deal of strength, this is the grade of bolt you should use.

5/9A bird's eye view into the ARP manufacturing facility. It takes specialized processes, machines, and highly trained people to build the specialized hardware required to supply the needs of racers.

There are many makers of bolts around the world, and some of these manufacturers are dedicated to making nuts, bolts, and studs exclusively for the racing industry. As racers, we are lucky to have people who make specialty fasteners for our industry. The bolts, studs, and nuts used on racing engines alone are unique and require a good deal of research and development to provide optimum performance in the intended application.

The infrastructure requirements needed to make special hardware are way beyond those of even the most resource-rich professional racing teams. It takes very specialized equipment and highly controlled processes, not to mention chemical processes and special material labs, to ensure quality and consistency from lot to lot. ARP makes a variety of very specialized fasteners for the racing industry. Chris Raschke works for ARP and has some unique insights regarding the use of nuts and bolts on race cars.

"The act of installing and removing the head bolts on an engine during the disassembly process can place undue stress on the threaded hole and the block," says Raschke. As racers, we have a tendency to take our cars apart and reassemble them as part of the maintenance and tuning process. This activity can cause excessive wear and tear on vital parts of the car. On engine surfaces for example, we take a great deal of time and incur some very high costs to make sure mating surfaces are flat and free from imperfections. Then we take them apart frequently.

6/9Header bolts have smaller heads to assist in installation. With headers, due to larger ports designed for maximum power, there is a limited amount of tool clearance left to properly torque the bolts. This design helps eliminate that problem.

The installation and removal of head bolts can also create burrs around the threaded areas, impacting the flatness of the surface. If the block is aluminum, the opportunity for damage is even greater. This added stress can be eliminated by replacing the OE bolts and the accompanying special washers and nuts with studs. Not only does the use of studs in this application reduce the wear and tear on the block, but they also generate more even load distribution of the clamping forces required to prevent head gasket failures. And, as an added bonus, they hold the gasket in place during the assembly process.

What other areas of the race car should get a better grade of hardware than was supplied as part of the OE package? Raschke has some good insight regarding what the racer should be looking toward when replacing hardware. "Any area that is subject to high maintenance (this equates to frequent assembly and disassembly), for example, bolts on the rearend that hold the third member in place, should be replaced with a stud kit," Raschke says. "This will speed gear changes and help prevent excessive wear of the threads in the axle housing. It also promotes better gasket sealing."

We need to remember that these stock components were not designed for the high frequency of use expected of racers. In the stock application, they were designed to be installed once at the factory and then last multiple years prior to any disassembly. As racers, we may remove these bolts several times on a race day, or at the very least, several times a month. There are multiple locations on your race car where it makes good sense to utilize studs and nuts versus a bolt alone.

7/9The use of studs in various locations is one way to prevent excessive thread wear in softer metals such as aluminum. It also helps speed up specific operations such as gear changes. The use of inexpensive hardware can save time at the track.

An area that deserves some real attention is the exhaust system, specifically header flange hardware. The exhaust on race cars goes through extreme variations in temperature. These changes can cause sealing issues as the gaskets expand and contract. This leads to exhaust leaks, and the hardware gets the blame. The last place where any problem should occur is in the exhaust system, especially if the problem is completely preventable.

Exhaust leaks may not be an issue with the hardware loosening up. It may be more traceable to gaskets being unable to seal after multiple expansion and contraction cycles. This is especially an issue with aluminum heads. The biggest problem here could be the inability to adequately tighten the bolts to the correct torque levels due to header tube interference. This problem may be resolved by using different hardware with smaller heads to help provide adequate tool clearances.

Still another area that we need to look at as the power levels increase is the interface between the engine, transmission, and drivetrain. The bolts and/or studs that secure the engine to the bellhousing and the bellhousing to the transmission need to be the best fasteners we can locate. The OE hardware is more than adequate when power levels never exceed several hundred horsepower, but the modern race engine, even at the weekend warrior level, can surpass 650 hp.

That level of output places a large amount of stress on the hardware, which can be compounded by the level of grip developed by the tires and the chassis. This can transfer very high loads to the hardware responsible for keeping the drivetrain together. The thought of using OE hardware is scary, to say the least.

8/9Stock rods are required in many divisions, but the rod bolts are open. It is the racer's option to upgrade the bolts to give them an extra margin of strength. The rod bolt is an application that can utilize the stretch gauge.

We should be using the best hardware possible in these critical areas. The superficial cost savings of using substandard hardware is not worth the economic risk. From a risk mitigation perspective, using quality hardware in these high-stress areas saves money and keeps you safe in the short term and the long term.

We have already established that bolts are basically springs, and the tension they apply to an interface is a function of the amount of force they can apply (i.e., clamping force). Racers joke about tightening a bolt until just before it gets loose again in order to get the most force out of it. While this may be good for some comedic relief, it is not even close to the truth.

Bolts have very specific torque requirements, and the ways to measure them are varied and a good subject for another article. If possible, consult the manufacturer of the bolt first. The SAE has developed some torque values based on the size and grade of the bolt. The intended application has a great deal to do with final torque values.

We measure torque to establish preload on the bolt or stud. Any excess friction between the bolt and the joining threads can skew the torque reading. The torque reading could be artificially high compared to the amount of actual bolt stretch. To minimize this condition, the threads need to be lubed. This lubrication can be accomplished in a variety of ways with a variety of products.

9/9Studs installed in an aluminum block. Their use allows greater durability of the parts and easier installation. When used with the correct precision washer and nut, studs actually do a better job of distributing clamping forces.

Some specialty bolt manufacturers have very specific recommendations for the lubricant. Consult with the manufacturer regarding its specific recommendations. If that is not possible, there are a number of products on the market for this specific application. Just make sure all of the threads are clean and free from any damage. In some applications, the threads may need to be assembled dry, which is why it is important to consult the manufacturer of the product you are dealing with to secure the company's recommendations.

The manufacturer of the product you are using has put a great deal of engineering into the product, so consult the manufacturer if there are any questions regarding torque values. Connecting rods are a good example. There is a good deal of information on how to generate sufficient clamping loads. The most popular method is to use a torque wrench to measure the force on the bolt or nut. While this may be the most popular method, there are better ways that eliminate any guesswork.

Measuring the amount of bolt stretch is really the best way to determine the correct load placed on the bolt. This requires special tooling (such as a stretch gauge), which is available to the racer for a reasonable price. However, you won't always be able to apply this method due to the limited clearances and accessibility to both ends of the bolt. That means the only other option left to the racer is a torque wrench.

While the bolt is a seemingly mundane and simple part of the modern race car, it is a complex and incredibly important component. The cost of bolts, nuts, and quality washers is a fraction of the cost of the complete car. If they are poorly matched to a specific task, they can cause catastrophic damage that can make the cost of the highest quality hardware seem insignificant in comparison. Knowing the risks, it just does not make sense to scrimp on hardware. Use the best and feel more confident at the racetrack.